In a parliamentary debate in the House of Commons, David Cameron said: "I ask the Labour government not to return to retribution and war on drugs. That has been tried and we all know that it does not work." That was in December 2002. And as a member of the home affairs select committee on drug misuse, Cameron supported the following recommendation: "That the government initiates a discussion within the Commission on Narcotic Drugs of alternative ways – including the possibility of legalisation and regulation – to tackle the global drugs dilemma."

That too was in 2002.

This week a major international summit on drugs will be hosted by Baroness Meacher in the House of Lords. No one from Downing Street will attend. No front line British politicians will be there to listen and learn from international medics, academics, politicians and economists who will reflect on lessons learnt from, and debate new approaches to, the "war on drugs".

Privately, senior politicians have encouraged the hosting of the event and told organisers that they are sympathetic to a new discussion about drugs legislation – but only once public opinion has shifted. They signal privately that there is a need for change, but do nothing to lead that debate.

Cameron and Britain's other leading politicians might do well to read the recent Global Commission on Drug Policy report (written by, among others, former UN secretary-general Kofi Annan, former US secretary of state George Shultz, and former Federal Reserve chairman Paul Volcker).

They made this plea: "Political leaders and public figures have the courage to articulate publicly that… the war on drugs has not, and cannot, be won." They then concluded: "Break the taboo on debate and reform. The time for action is now."

The taboo shows no sign of being broken by Britain's spineless political class, despite this generation of leaders being the first to have widespread, first-hand experience of illegal drugs. They will undoubtedly have come across cannabis, cocaine and ecstasy throughout their university, social and professional lives. Some of their best friends – and colleagues – will have taken them.

But from Messrs Cameron, Clegg, Miliband or even George Osborne – who might take a particular interest in the tax-raising possibilities of a regulated drug market, as we disclose in today's Observer – we hear nothing.

Instead, the leading voices in calling for a new discussion about the war on drugs are coming from Latin America. In today's Observer, Colombia's President Santos speaks eloquently about the price his country has paid as a drug "producing nation" servicing the demand for illicit drugs in "consumer nations", principally in Europe and the US.

He and President Calderón of Mexico are increasingly vocal about the need to look again at a war that is showing no signs of being won – ever. Drug consumption and availability are not abating, they are on the rise. As Santos says: "The world needs to discuss new approaches… we are basically still thinking within the same framework as we have done for the last 40 years."

Santos speaks with some moral authority given the carnage visited on his country over the last 30 years. He has gone further than any incumbent. In today's Observer interview he raises the prospect of a regulated market for marijuana and perhaps even cocaine. But he is insistent that this can only come through international consensus.

Those in the "producing nations" in Latin America are increasingly impatient at having to suffer the bloodiest collateral damage in the service of the consuming nations. President Calderón recently hit out at the US and said: "We are living in the same building. And our neighbour is the largest consumer of drugs in the world and everybody wants to sell him drugs through our doors and windows."

It is unconscionable for the leaders of the largest consuming nations – the US, UK and Spain – to remain silent any longer. The habits of their citizens are not only directly responsible for the wasted lives of many Latin Americans but, as President Santos says, are now culpable in the destruction of the Amazonian rainforests as coca producers move to ever more remote parts of Colombia to harvest the raw material of cocaine.

The war on drugs has failed. When policies fail it is incumbent on our leaders to look for new ones. They show no signs of doing so – even as Latin America's body politic is threatened by the tentacles of the narco gangs who pay off politicians, judges, journalists and policemen – or just kill them, so that they can better transport drugs to us.

Prohibition has failed. As we noted last year: "If the purpose of drug policy is to make toxic substances available to anyone who wants them in a flourishing market economy controlled by murderous criminal gangs, the current arrangements are working well." Milton Friedman was right, 20 years ago, when he said: "If you look at the drug war from a purely economic point of view, the role of the government is to protect the drug cartel. That's literally true".

Plenty of leading British figures and institutions agree that prohibition has failed. The ex-president of the Royal College of Physicians, the ex-chairman of the Bar Council, the Police Foundation, the Royal Society of Arts and numerous others have questioned whether prohibition works. The roll call of international figures who have called time on the drugs war is long and distinguished.

But from leading British politicians? Nothing. They are being left behind by public opinion both here and abroad. A poll commissioned last year by Liberal Democrats for drug policy reform found that 70% were in favour of legalising and regulating cannabis. These views are no longer the preserve of students, stoners and slackers. If none of our political leaders has the courage to speak out independently and engage the debate, maybe they can summon the wherewithal under the cloak of an all-party commission into the regulation of drugs. That would be a start.

But it is looking increasingly unlikely that it will be politicians who spark a debate about a new approach to the failed war on drugs. The winds of change will not likely be driven by politics, health or morality, but by economics. Business will be the prime mover.

Over the course of the last 40 years, America has spent $2.5tn on the drugs war. As the Global Commission makes clear, "in a time of fiscal austerity, we can no longer afford to maintain multibillion-dollar investments that have largely symbolic value".

In the States, in so far as any debate is taking place, it is being stoked by economists and the business community who see an economic case for ending the drug war on the one hand, and for opening up a lucrative new market for American business on the other. The Economist has argued for the legislation of drugs for more than 20 years.

Six years ago, Forbes – America's business bible – published the names of 500 prominent businessmen and women who favoured a regulated drugs market. In the States people are starting to ask why the market in drugs can't shift from the cartels to the capitalists.

In a free and open market, the legitimate and very real concerns of many Britons can be played out publicly as they have been with alcohol and smoking – to great effect, particularly in the case of smoking.

When the debate changes substantively both here and in the States it will do so because, while politicians may keep their counsel and remain silent, money talks.